A desk weighing 80 N rests on the floor. The coefficient of friction between the floor and the desk is 0.25. What is the frictional force between yhe desk and the surface of the floor?

Answer 1

The friction force is
M*g*Uk
IF the desk is moving. Uk is the kinetic friction coefficent in this case.

The problem should have told you if the desk is moving, and whether the coefficient of friction is static or kinetic.

If the desk is not moving, the applied force equals the friction force.